Testing biodigester effluent is also important in order to know how effective it is as a fertilizer. Many farmers rely on manure from their animals and biodigesters take this animal manure to produce gas. Making sure the resulting biodigester effluent can also be used as a fertilizer with equal or better results to that of traditional or commonly used fertilizers is extremely important to insuring that the biodigester can become an integrated addition to the farm.

Background

Testing is being done by the Laboratorio de Ajusco de Tecnologia Alternativa, a nonprofit laboratory providing technical assistance in testing different appropriate technologies. Right now they are working with Isla Urbana for rainwater quality testing and the International Renewable Resources Institute-Mexico for biodigester effluence water and fertilizer quality studies.

The International Renewable Resources Institute and Biobolsa wanted to test their biodidgester systems for fertilizer quality and applicability. This is part of a testing series for biodigester effluence the accompanying testing is on water quality of biodigesters.

Fertilizer Quality Expectations

Soil Basics

• Soil is a complicated matrix of many minerals and nutrients not completely understood by science, the following is a break down of what is understood thus far. Soil is composed of a balance of at least 6 macro and 6 micro elements. The 6 macro elements are nitrogen(N), phosphorous(P), potassium (K), calcium, magnesium, and sulphur. The 6 micro elements are iron, maganese, boron, copper, zinc, and molybdenum.^[1][2] This list is continually extended as new minerals and exiting minerals and micro nutrients roles within soil are better understood by science.
• There are different N:P:K ratio's recommended specific for each crop and for different stages of growth including: seedlings stage, vegetative stage, and flowering and fruiting stages. So your soil and fertilizer mix should change depending on the plant and the stage its in.^[3]
• Seven additional nutrients beneficial to plants, but considered only psuedo-essential, include sodium, cobalt, vanadium, nickel, selenium, silicon, and aluminum.^[4] The nutrients available from minerals in the soil differ in: how they're absorbed and utilized by the plant, their mobility in the plant, and the symptoms expressed in the plant from deficiency or excess amounts of the nutrient.^[5]
• Soil structure is another important factor in soil quality and plant yield. The soil structure can be qualitatively analyzed by just visually and physically feeling the texture of the soil. Soil structure effects the soil's permeability, susceptibility to erosion, root growth, and the ability of soil to retain nutrients. While synthetic fertilizers fail to renew and rebuild soil structure, composted manures and foods scraps have the ability to add to and renew the soil structure. Testing biol's ability to build up soil structure is another important quality assessment.

Parameters List

Different Nutrients and Their Functions for Plants

6 Macro Elements

Macro Nutrient Concentration Limits

^[6]

1.Nitrogen (N)

• is found in chlorophyll and protoplasm in plants and is an important component in proteins.
  
• Excess nitrogen shows as lush soft growth and can result in a significant yield loss through weakened stem and flattening of crop by wind and rain, failure to ripen, and increased susceptibility to pests and diseases.^[7]
• Deficiency shows as a shortening of stems and yellowing of leaves.
  
• Plants that are high nitrogen feeders include: squash, cabbage, broccoli and corn.
• Most nitrogen in the world exists in our atmosphere as N2, which is not available to most plants for use, thus it is important to find and measure the amount of bioavailable nitrogen.^[8]
  

' Bioavailable Nitrogen

Nitrate, NO3-

• Nitrates are an important nutrient for plants. Crops such as tobacco, potatoes and tomatoes prefer nitrate as their source of Nitrogen. Nitrates are transformed from nitrites, NO2-, by nitrifying bacteria and Ammonia can be oxidized into nitrates or nitrites.^[9] Fertilizers in nitrate form are susceptible to potential leaching and losses through gaseous emissions during

dentrification or nitrification.^[10]

• In excess (at about 5 milligrams per liter) nitrates in lakes and streams can lead to excessive growth of alga, eutrophication, and thus a loss of dissolved oxygen. Reduced levels of dissolved oxygen can cause fish deaths as well as reduced growth of native plant vegetation.^[11]
• Animals and humans cannot use inorganic forms of nitrogen and if nitrate does exceed 10 milligrams per liter in drinking water, it can cause interfere with blood-oxygen levels and lead to methemoglobinemia (or blue baby syndrome) in infants and gastric cancer.^[12][13] *Leafy vegetables in particular, under different environmental condition's, can accumulate nitrates to potentially harmful concentrations. These vegetables include Brassicaceae (rocket, radish and mustard), Chenopodiaceae (beetroot, Swiss chard and spinach), Amaranthaceae (Amaranthus), Asteraceae (lettuce) and Apiaceae (celery and parsley).

The general limits of nitrates from leafy vegetables and drinking water is 100-170 mg/day of human consumption.^[14]

• Summary: While reducing nitrate levels is an important factor in measuring effluent being returned to rivers and streams, having higher nitrate levels can be a benefit for fertilizer applications on crops as long as the nitrate levels in the fruits and veggies themselves remain below limits required for human consumption levels. This can mean that nitrate application is better for crops in their seedling and vegetative stage, while application should be reduced during the flowering and fruiting stage. Also their should be a crop specific application of nitrates, where leafy vegetables receive lower rates of nitrate application.

Nitrite, NO2

Nitrite is not bio available, but must be converted into nitrate for use by plants. Small concentrations of nitrite can be toxic to plants, but nitrite is an important intermediate in the conversion of ammonium to nitrate in the soil. Nitrite is also formed by dentrification, or the bacterial reduction of nitrate to nitrite, this occurs under anoxic (or oxygen deprived) conditions. Nitrite is not a stable intermediate and very few cases of nitrite accumulation have been reported. The levels of nitrite usually do not exceed 0.25 to 70 ppm within soil. Accumulation however can occur in neutral or alkaline soils, since the conversion from nitrite to nitrate is inhibited more than the conversion of ammonia to nitrite.^[15] Also bacteria present in sewage sludge converts nitrates into nitrites.^[16]

Ammonia, NH3

Ammonia is not bio available but must be converted into Ammonium for uptake by plants. This is very volatile and needs to be transformed into other forms of nitrogen like urea for storage. Ammonia is the pungent smell from composts with too much nitrogen and not enough carbon. Ammonia is also the form of nitrogen most commonly converted into synthetic nitrogen compounds, like nitric acid, for industrial fertilizer applications.

Ammonium, NH4+

Ammonium is just as available to plants as nitrate, however ammonium usually does not accumulate into the soil because it readily is converted to nitrate in most conditions.^[17] Ammonium is less able to leach from the soil, however it is very volatile and can easily escape in aerobic environments.^[18] Ammonium can be toxic in high enough concentrations and for this reason plants usually do not readily uptake this as readily as nitrate.

Organic nitrogen

• This is measured by the Total Organic Nitrogen, which does not account for inorganic forms of nitrogen like (NH4, NO3, NO2)
• Urea, (NH2)2CO, urea is an example of organic nitrogen and it is produced in the body principally for nitrogen excretion. Urea contains about 88 percent of the N (nitrogen), up to 67 percent of the P (phosphorus) and up to 71 percent of the K (potassium) present in human excreta.^[19] When urea is applied to the soil it reacts with water to form ammonium within 2 to 3 days. If urea is soly applied to the surface of soil some volatilization of the ammonia will occur and this can be fairly drastic in summer months.^[20]

Total Kjeldahl Nitrogen (TKN)

Total Kjeldahl Nitrogen is the sum of organic nitrogen, ammonia (NH3), and ammonium (NH4+).

Total Nitrogen

Total Nitrogen can be derived by finding total kjeldahl nitrogen (TKN), ammonia, and nitrate-nitrite and adding them together. Total Nitrogen does not include N2, which is not bioavailable.^[21]

2.Phosphorous (Ph)

• makes up the structural framework of RNA and DNA, is used to transport cellular energy in biological organisms, and forms into phospholipids, which become the main structural components of cell membranes.
  
• Excess phosphorous can interfere with plant uptake of copper and zinc.
  
• Deficiency of phosphorous creates thick small cells, when looking at the new growth at the tips of the leaves this may look like fungus to some.
  
• Phosphorous is not found free in nature, but is excavated from minerals, rivers passing over rock with these minerals or rain coming in contact with these minerals helps erode the rock and release this phosphorous to be used by biological organisms. In 2008 based on the rates of excavation, scientists claimed that "Peak Phosphorous", where phosphorous reserves run out, could occur within 30 years due to the increasing use of crop based biofuels. This has been reflected in the skyrocketing cost, where the raw material of phosphate has increased by 700 percent to the price of $367 per tonne.^[22]

Phosphate Phosphorous Is concentrated in soils by manures from seed eating birds.

Potash Phosphorous

Is concentrated in soils by burnt and rotted plants or composts.

3.Potassium (K)

• helps activate 60 different enzymes involved in plant growth, it helps stabilize the pH between 7 & 8, regulates the opening and closing of stomats, thus also regulating the exchange of CO2, water vapor, and oxygen essential for photosynthesis, water and nutrient transport, and plant cooling. It also helps regulate the transport of sugars, the synthesis of starch, and the synthesis of proteins.^[23]
• Excess can induce a magnesium deficiency and micro nutrient deficiencies in iron and zinc.^[24][25]
  
• Deficiencies may result in leaves turning purple, stunted plant growth, and delay in plant development.^[26]
  

Nitrogen, Potassium, and Phosphorous values for different Fruits and Veggies

1. • ^[27]

4.Calcium (Ca)

• is essential for growth and cell structure in plants as well as acting as a secondary messenger for plant uptake and plant responses to environmental conditions. Without calcium plant cell membranes deteriorate.^[28]
• Excess may cause deficiency in magnesium or potassium.
• Deficiency may cause reduced growth or death of leaf tips; blossom-end rot of tomato; and poor fruit development.^[29]
  
• Calcium is removed by salinization (or salt) in drylands and deserts. Over irrigation in drylands causes irrigation water to evaporate, leaving behind increased amounts of salts. When this sodium is present in soils it suppresses the uptake of calcium by plants.^[30]

5.Magnesium (Mg)

• is essential to forming basic nucleic acids and thus essential to all cells of all known living organisms. 300 enzymes rely on the presence of Mg for catalysis including synthesis and utilization of ATP, DNA, and RNA. Magnesium is also an important component in chlorophyll.
• Excess in imbalance with calcium and potassium may reduce growth. Look at the table below for balancing the major ions in soil.
• Deficiency results in the yellowing of leaves between leaf veins and poor fruit development and production.^[31]
  

6.Sulphur (S)

• important polypeptides, proteins, and enzymes are made of amino acids containing sulfur. Sulfur also helps form disulfide bonds (S-S bonds), which plays an important role in the folding and stability of some proteins.
• Excess can cause premature dropping of leaves and harmful changes in the metabolism of plant cells.^[32]

• Deficiency have yellow leaves, produce fewer seeds and appear to be more susceptible to disease, with similar symptoms to nitrogen deficiency however the effects occur on new growth.^[33]
  

6 Micro Elements

Concentration Limit for Micro Elements in Waste Water Agricultural Application

^[34]

Concentration Limit and Availability in Soil

^[35]

Balancing Proportions between Major Ions in Soil

^[36]

1.Iron

• aids chlorophyll synthesis
• Deficiency results in yellow or white spots between the veins of new leaves, which is followed by dead leaf tissue.
• Excess results in bronzing leaves and tiny brown dots.

2.Maganese

• Activates enzymes
• Deficiency results in yellowing between veins and mottling of young leaves.
• Excess results in brown spotting surrounding by a chlorotic circle on older growth.

3.Boron

• Forms part of Cell wall
• Deficiency can result in the death of new growth and leaf deformation with areas of discoloration.
• Excess results in yellowing of leaf tips followed by the premature death of cells and new tissue giving a scorched appearance to leaves.

4.Copper

• Component of enzymes

5.Zinc

• Activates enzymes
• Deficiency can result in yellowing of veins in young leaves and stunted leaf size.
• Excess can result in iron deficiency in some plants.

6.Molybdenum

• Involved in Nitrogen fixation

Other Parameters for Concern in Waste Water Agriculture Application

Expected Parameter Concentrations of Influent and Effluent Water Quality from Biodigester

• Bui Xuan, An; Preston, TR; and Dolberg, F, 1996. The introduction of low-cost polyethylene tube biodigesters on small scale farms in Vietnam, Livestock Research for Rural Development, 8:1.
  • Bui Xuan, An. The Role of Low-cost Plastic Tube Biodigesters in Integrated Farming Systems in Vietnam. Livestock Feed Resources within Integrated Farming Systems. Pg 277-294. http://www.fao.org/ag/againfo/resources/documents/frg/conf96pdf/an.pdf

pH

The pH of soils is one of the most important properties that effects nutrient availability.

• The 6 Macronutrients are less available in low pH soils.
• The 6 Micronutrients are less available in high pH soils.^[37]

E. Coli

Testing for coliform bacteria is cheaper and a lot faster than testing for specific organisms and pathogens, thus the U.S. Public Health Service created a standard in 1914 for coliform concentration as an indicator of overall microbiological suitability of drinking and surface waters. 1 fecal coliform/ 100ml = 1 ppb = 0.001 ppm.

Sodium, Na

High concentrations of sodium ions found in waste water and used to irrigate agricultural areas reduce the infiltration rate and permeability of soils. When these soils dry a crust forms creating problems for tillage and interfering with germination and seedling emergence. These effects are dependent on the sodium ion concentration relative to the concentration of calcium and magnesium ions and the total salt concentration. Since the total salt concentrations in sewage effluent can be several hundred mg/l higher than in drinking water, total salt is an important indicator of the quality of fertilizers and irrigation waters from sewage.^[38] SAR, Sodium adsorption ratio.

Soil Structure

Soil structure (whether porous or compacted) effects the soil's permeability, susceptibility to erosion, root growth, and the ability of soil to retain nutrients. While synthetic fertilizers fail to renew and rebuild soil structure, composted manures and foods scraps have the ability to add to and renew the soil structure. The structure depends on the soil composition of sand, silt, clay, and organic matter in the soil as well as the presence of any flocculating or ionic substances.^[39]

The soil structure can be qualitatively analyzed by just visually and physically feeling the texture of the soil. Another test for soil structure can be done by placing a soil sample in a tall mason jar filled with water and after shaking vigorously allow the particles to settle out over a day. The different components will stratify, with gravel ans sand falling to the bottom, silt above that, clay above that, organic particles above that, and just water at the top clear area. Testing biol's ability to build up soil structure is an important quality assessment.

Testing Biol Samples

Lab Testing

• Dry or refrigerate your soil samples immediately to stop soil microbes from continuing to alter nitrogen levels.^[40]

Field Testing

• A learning-based approach to field testing managed by local farmers can help increase adoption rates among farmers and ensure the appropriateness of the technology and application. This has been seen by The International Potato Centre in Lima, Peru. During the first cropping season farmers could learn about biol application rates in comparison to other available fertilizers as well as soil basics. During the second season a Farmer Field School could come in to encourage farmers to use and experiment with the concepts learned from the first season. Farmer involvement in testing ensures that the technology is appropriate for their specific needs and situation as well as speeding up the adoption process.^[41]

References